1. Field of the Invention
The present invention relates to the selective removal of more highly unsaturated compounds from mixtures of unsaturated compounds. More particularly the invention is concerned with the selective hydrogenation of acetylenic compounds from mixtures with dienes, such as 1,3-butadiene. The invention provides both novel catalysts and process for the selective hydrogenation of acetylenes in admixture with other unsaturated compounds.
2. Related Information
Supported copper catalysts and palladium catalysts have been preferred catalysts in cleaning up acetylenic impurities in olefin streams by selective hydrogenation. Copper catalysts selectively hydrogenate acetylenic compounds without substantial hydrogenation of the olefins and diolefins (designated herein as selectivity for retaining olefins), but have relatively low activity and short cycle time due to primarily polymer deposition on the catalyst surface. Palladium catalysts have excellent activity and much longer cycle time, but lower selectivity for the acetylenes than copper-based catalysts. To improve olefin selectivity of palladium catalyst, silver or gold has been added to palladium catalyst in minor amounts as modifier.
Fr 1 253 947 (1960) disclosed the copper catalyst for selective hydrogenation of acetylenic compounds in diolefin or monoolefin streams. The selective hydrogenation was carried out in vapor phase. 99.9-99.999% purity copper was supported on high surface area (25-300 m2/g) supports such as gamma alumina. Copper content of the catalyst was in a range of 5 to 20%. The catalyst may contain less than 0.1% other metals (based on metal content of the catalyst) such as Fe, Ni, Ru, Rh, Pd, Ir or Pt as promoter. The selective hydrogenation was carried out in both vapor and liquid phase. U.S. Pat. No. 4,440,956 (1984) and U.S. Pat. No. 4,493,906 (1985) disclosed the improved copper catalysts supported on the very specific alumina such as gamma alumina prepared from aluminum alkoxides, which are useful for removing alkynes in liquid hydrocarbon streams. The patentee characterized the gamma alumina as having 60 to 90% of pores which should have a pore diameter between about 40 xc3x85 and 120 xc3x85, and not more than 25% nor less than 2% had pore diameter between 1000 xc3x85 to 10,000 xc3x85. The nitrogen surface area of the alumina was from about 68 to 350 m2/g. The catalyst contained 3 to 13 weight % Cu. The catalyst contained minor amounts of at least one polyvalent activator metal selected from the group consisting of silver, manganese, cobalt, nickel and chromium. High purity of alumina, especially in terms of sodium (should be less than 0.15 wt %) and Fe2O3 (less than 0.06 wt %) contents, was claimed to be critical due to shrinkage of the surface area caused by frequent catalyst regeneration.
Ger 2 109 070 (1970) disclosed copper (26%)-zinc oxide catalyst for selective hydrogenation of acetylenic compounds in 1,3-butadiene stream in vapor phase.
U.S. Pat. No. 4,174,355 (1979) disclosed a process for removing (xcex1-acetylenes from diolefin streams by nonselective hydrogenation. The alkynes were removed by contacting the feed steams with CuO and or Ag2O supported on (xcex1-alumina in the absence of hydrogen or oxygen.
U.S. Pat. No. 4,533,779 (1985) disclosed palladium/gold catalyst supported on supports such as alumina (1 to 100 m2/g) for selective hydrogenation of acetylenic compounds. The contents of palladium and gold in the catalysts were in the range of 0.03 to 1 weight % and 0.003 to 0.3 weight %, respectively.
U.S. Pat. No. 4,831,200 (1989) disclosed the process for the selective hydrogenation of alkynes in olefin streams such as mixtures with 1,3-butadiene. The selective hydrogenation was carried out in two steps in sequence. In the first step, the hydrocarbon feed was passed at least partially in liquid phase with hydrogen over the palladium catalyst such as that disclosed in U.S. Pat. No. 4,533,779 discussed above. In the second step, the product stream from the first step was passed again at least partially in liquid phase with hydrogen over the copper catalyst such as that disclosed U.S. Pat. Nos. 4,493,906 and 4,440,956 discussed above to produce significantly reduced alkyne concentration in the final product stream.
U.S. Pat. No. 5,877,363 (1999) disclosed the process for the selective hydrogenation of acetylenic impurities and 1,2-butadiene in mixed olefin rich C4 streams by using supported hydrogenation catalysts such as Pt and Pd.
In general, the palladium catalysts are very active compared with the copper catalysts for selective hydrogenation of acetylenic compounds in the olefinic steams. But the palladium catalysts exhibit low selectivity for retaining diolefins, such as 1,3-butadiene, when one is trying to remove high concentrations ( greater than 2000 ppm) of total alkynes to less than about 500 ppm total alkynes in the streams, especially when the acetylenes are reduced to less than 200 ppm. The non selectivity of palladium catalysts is not desirable in commercial practice, because it resulting in a loss of 1,3-butadiene.
On the other hand, the copper catalysts are highly selective in retaining diolefins such as 1,3-butadiene by being very selective to acetylenes hydrogenation. But the activity of copper catalysts is slow. And the catalyst cycle time is undesirably short for the feed streams, which contain higher than about 2000 ppm total alkynes due to fast deactivation caused by the deposition of polymeric material on the catalyst surface, Even though the hydrogenation is carried out in liquid phase, some of the polymers deposited on the copper catalyst has little solubility in the liquid product stream under the selective hydrogenation condition. Due to these two reasons, the copper catalysts need improvement for the selective hydrogenation of the mixed olefin feeds, which contain relatively high concentration of total alkynes.
The present invention includes a catalyst comprising a copper component containing from about 0.1 to 25 wt percent Cu, preferably 0.2 to 20 wt %; a palladium promoter in a range of 0 to 2 wt %, preferably 0 to 1 wt %; a silver or gold modifier is in a range of 0 to 15 wt %, preferably 0 to 10 wt %; and a zinc oxide modifier is in a range of 0 to 25 wt %, preferably from 0 to about 15 wt %. The silver modifier moderates the catalyst activity, and improves the olefin yield and the cycle time. The zinc oxide modifier improves the olefin yield such as 1,3-butadiene with small improvement in the catalyst activity. The zinc oxide modified copper catalysts is especially very effective for removing vinyl acetylene impurity with extremely high yield of 1,3-butadiene. In a preferred embodiment the catalyst components are deposited on a support.
The preferred supports have the average pore diameter larger than about 200 xc3x85, no micro pores, total pore volume larger than about 0.65 cc/g, and preferably less than about 230 m2/g BET surface area. The copper catalysts are preferably promoted with the Group VIII metal such as palladium to improve low activity of copper catalyst. The product stream typically contains less than 20 ppm total alkynes. Also the copper catalysts and the palladium promoted copper catalysts may be modified with zinc oxide to improve the performance of the catalysts. The reactor was loaded with two or more copper catalysts promoted with different levels of palladium. Preferably the copper catalysts were also modified with silver, gold or both silver and gold to reduce polymer formation by the copper component of the catalyst, improve the yield of olefins such as 1,3-butadiene, and prevent the loss of copper and palladium due to leaching out into the liquid phase of hydrocarbon.
The process of removing acetylenic compounds by contact hydrocarbon streams containing small amounts of acetylenic compounds with the catalyst of the invention in various arrangements and configurations is also part of the present invention.